Tender boxes, as they are commonly known, are suspended by mobile cranes or similar hoist devises to provide a stable working platform, which can be positioned next to various structures, such as buildings, towers and bridges. In many applications, tender boxes suspended from mobile cranes are safer and more versatile than conventional scaffolding. The construction and maintenance of communication towers and bridges are especially well suited for the use of mobile cranes and suspended tender boxes. A crane can position a tender box at various heights as well as quickly reposition the tender box to different locations. When properly tethered, tender boxes are generally more stable and safer with respect to handling construction materials between the ground and the elevated work area.
Conventional tender boxes have several disadvantages. Generally, cranes have difficulty positioning the tender boxes at the appropriate distance from the vertical structure. This problem is often complicated by strong wind gusts, even when the platforms are properly tethered. In addition, the rigger platform or work deck of conventional tender boxes carries not only the worker but the materials and equipment. The crowded work deck is a potential hazard. Uneven weight distribution on the work deck can cause the deck to tilt even when properly tethered.
The United State Occupational Safety and Health Agency (OSHA) sets various safety standards and operational requirements for suspended tender boxes. OSHA requires that the work deck be enclosed on all sides by a railing to prevent workers from falling between the inner edge of the rigging and the work face of the structure. Also, OSHA regulations require that after every repositioning of the mobile crane or hoist device, the tender box must be tested by raising and lowering a test load to the maximum operational height before resuming operation. Consequently, every repositioning of the crane requires the tender box to be unmanned, loaded with the test weight, raised and lowered, and then manned before work can resumed.